The present invention relates to methods for modifying the surface of hydrophobic and/or oleophobic coatings and, in particular, to surface modification of hydrophobic and/or oleophobic coatings on ophthalmic lenses.
Ophthalmic lenses are commonly provided with coatings that impart improvements to lens performance, such as scratch resistance, anti-reflection, anti-static, and other properties. It is also common to apply more than one of these coatings to the lens to provide some combination of improvements in performance characteristics. A final anti-soiling coating is often applied on top of these other coatings, and has hydrophobic and/or oleophobic properties to protect the inner coatings from moisture and to improve the ease of cleaning the surface of the lens. Generally, the hydrophobic and/or oleophobic coating is comprised of compounds, such as fluorinated compounds, that exhibit relatively high water wetting angles, generally in excess of 90 degrees. Typically, such hydrophobic and/or oleophobic coatings also reduce friction and create a slippery or slick surface on the lens.
Most, but not all, manufacturers of ophthalmic lenses apply anti-reflective and/or anti-static and/or anti-soiling and/or hydrophobic and/or oleophobic layers after surfacing the lenses to meet a particular prescription requirement or after applying a scratch resistant coating to the lenses. The final stages of lens processing often include the application of a stamped layout ink mark on the surface of lens, which provides information regarding, among other things, the fitting position and optical orientation, including the horizontal reference axis of the lens. This information is required for the proper grinding or edging of the lens to the final shape needed to fit the lens into a chosen frame and have it in proper optical alignment for the patient.
The ink marking operation is commonly performed using the “pad printing” method. The lens is first oriented and held in position on the marking platform. This alignment is essential to assure that the ink marking is applied in the correct position to reflect the optical orientation of the lens. Layout marking ink is transferred from an inked marking plate by means of a soft rubber pad, such as a silicone pad, and subsequently applied to the lens. Once the lens is marked for layout, the lens is checked for ophthalmic properties and/or prepared for the edging operation.
The ink markings are used for proper alignment of the lens during the edging operation. Typically, an edging pad having an adhesive on both sides is placed on the front surface of lens so one side of the pad adheres to the lens surface and the second side adheres to an edging block that is properly aligned to maintain lens orientation during the edging process. The assembly consisting of the lens, edging pad and edging block, is then placed in the edging machine chuck assembly, and the lens is held between sections of the lens holding spindle of the edging machine. The lens orientation is maintained by the block which must stay in firm contact with the lens surface during the edging operation.
The lens is edged by rotating the lens through controlled rotation of the spindle of the edging machine. One method of edging utilizes a diamond impregnated wheel, also rotating with a controlled speed, that contacts the edge of the lens, grinding the lens in order to reduce the diameter of the lens. The lens is edged according to frame shape and optical orientation, and can be subsequently finished with an edge groove or drilled with mounting holes, depending on frame type and shape.
The optical performance of a lens depends on how accurately the lens is fitted into the frame. In order to achieve the proper fitting, it is essential that the lens is clearly and accurately stamped, and does not slip during the edging operation. However, the hydrophobic and/or oleophobic coatings often make the lens surface slick or slippery. Furthermore, it is very common to make the surface of lenses as slippery as possible to enhance cleaning. This slippery coating can reduce the adhesion and coverage of the ink stamped on the front surface of the lenses, and also can reduce adhesion of edging pads to the lens surface resulting in slippage of the lenses during the edging operation.
To achieve accurate and complete ink markings on the lens surface used for layout and to edge the lenses more accurately, it is desirable to modify the surface properties of the hydrophobic and/or oleophobic coating to enhance the ability to stamp the lens surface and to reduce slippage during the edging process, while still providing good lens cleaning properties and protection of the inner anti-reflective coating layers and/or other coating layers on the lens.